Roof bolting and column building for solution mining

ABSTRACT

A well is drilled down to the mineral deposit to be mined. The mineral deposit is penetrated by the drill bit so that about 10 percent of the total thickness of the mineral deposit is exposed to the wellbore. A given volume, the size of a required cap for the roof bolt, is washed out about the wellbore and hanging wall of the mineral deposit. The cap and bolt are formed by introducing casing and cementing it and the washed out area to the roof of the soluble material. After the bolt has been set, the cap is drilled through and solution mining progressed. The mineral is washed away from the cement cap leaving a capped roof bolt to inhibit roof slouching. Columns may be formed by washing a cylindrical area to the foot wall by progressive lowering of the washing tube into the mineral deposit and sealing a perforated liner to the footwall. A permeable cement or an impermeable cement which is subsequently perforated may be used as the sealant so that fluid may flow freely from the wellbore to the mineral deposit. The mineral is then washed by introduction of washing fluid through the perforated liner and permeable column into the mineral formation.

United States Patent [72] Inventor Donald W. Dareing Fayetteville, Ark.[21] Appl. No. 866,873 [22] Filed Oct. 16, 1969 [45] Patented Aug. 17,I971 [73] Assignee Cities Service Oil Company 54] ROOF BOLTING ANDCOLUMN BUILDING FOR SOLUTION MINING 10 Claims, 3 Drawing Figs.

[52] US. Cl 299/5, 299/1 1 [51] Int. Cl E21b 43/28 [50] Field otSearch..299/5, 4, ll

[56] References Cited UNITED STATES PATENTS 2,038,757 4/1936 O'Donnell299/5 3,018,095 1/1962 Redlinger Primary ExaminerErnest R. PurserAttorney-J. Richard Geaman ABSTRACT: A well is drilled down to themineral deposit to be mined. The mineral deposit is penetrated by thedrill bit so that about 10 percent of the total thickness of the mineraldeposit is exposed to the wellbore. A given volume, the size of arequired cap for the roof bolt, is washed out about the wellbore andhanging wall of the mineral deposit. The cap and bolt are formed byintroducing casing and cementing it and the washed out area to the roofof the soluble material. After the bolt has been set, the cap is drilledthrough and solution mining progressed. The mineral is washed away fromthe cement cap leaving a capped roof bolt to inhibit roof slouching.Columns may be formed by washing a cylindrical area to the foot wall byprogressive lowering of the washing tube into the mineral deposit andsealing a perforated liner to the footwall. A permeable cement or animpermeable cement which is subsequently perforated may be used as thesealant so that fluid may flow freely from the wellbore to the mineraldeposit. The mineral is then washed by introduction of washing fluidthrough the perforated liner and permeable column into the mineralformation.

PATENTEU AUG 1 7 IQYI FIGURE I FIGURE 2 FIGURE 3 D.w. DARE 1 N6INVENTOR.

- ROOF BOLTING AND COLUMN BUILDING FOR SOLUTION MINING BACKGROUND OF THEINVENTION This invention relates to the supporting of overburden strataduring solution mining of soluble materials in subterranean formations.More particularly, it relates to a novel method working the forming of aroof bolt and column firm which the overburden may be supported duringsolution mining of mineral deposits from subterranean formations.

In solution mining of mineral deposits the hanging wall (roof) andfootwall (floor) of the seam of mineral may consist of firm and coherentrocks. The working area need not be supported and will remain firmthroughout the solution mining operation. More often, however, the roofrocks are not rigid and will cave or warp from the pressure of theexposed overburden. Support is then required to prohibit roof caving andpremature breaking down of the mineral seam. Some rocks maintainthemselves over a large area for long times and then cave suddenly andunexpectedly. Others are elastic and sink gradually and regularly. Stillothers are plastic or loose and sink quickly when undermined. In allcases it is necessary to provide the proper support to sustain acompetent solution mining operation.

The coherence of the overburden depends upon rock pressure, the roofpressure, and the areal extent of the proposed solution miningoperation. As roof pressure manifests itself only after a short intervalof time, this length of time is dependent upon the degree of fissuringand loosening of the rock. The excavation must be supported immediatelyafter the roof area is washed to prevent the development of stresseswhich will eventually cave the overburden.

A variety of methods have been employed in which roof bolts and columnsare used in subsurface mining. These techniques, however, are normallyconstructed by mine workers working underground to prevent slouching andcave-ins for the protection of the miners. Conventional supportingtechniques consist of pillars of unmined rocks, timbering props, cribs,forepoling, stowing and various and sundry other methods. Conventionalsupporting techniques, however, are not practical for solution miningoperations as they require mining personnel to construct them in thesubsurface. Many mineral deposits of economic value exist at depthswhich are impractical for conventional mechanical mining, for examplesulfur, phosphates, uranium and metallic salts, but solution andrecovery of which will result in caving of overburden without propersupport.

It is an object of my invention, therefore, to provide a novel methodfor the supporting of underground structures.

It is another object of my invention to provide for a method of roofbolting the overburden formation during solution mining operations.

Another object of my invention is to provide for a method of supportingthe overburden by columns during solution mining operations.

It is still a further object of my invention to provide for a method ofroof bolting and column supporting overburden during solution miningoperation, whereby the economic recovery of the mineral is afforded overa greater extent of the deposit than by use of conventional unsupportedsolution min- SUMMARY OF THE INVENTION The present invention comprises amethod of construction for the supporting of overburdened rock duringmining of subterranean mineral deposits. Initially a well is drilledinto the mineral deposit. Generally percent of the total thickness ofthe mineral deposit will be a sufficient penetration. The area about thewell exposed to the mineral deposit is then washed until a sufficientvolume of material, the size of the required roof bolt cap, is removed.Casing is then introduced into the well and cavity so as to form anannulus between the well wall and casing. The annulus is then filledwith sealant to form a roof bolt which will support the overburdenedrock from caving or slouching during the subsequent mining'operation.

With these and other objects in mind the invention will be apparent fromthe drawings and description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevationview of the well drilled slightly into the mineral deposit depicting thewashing process for the area of the roof bolt.

FIG. 2 is a cross-sectional elevation view of theroof bolt, cap and thecontinued washing of the mineral deposit to form the column cavity.

FIG. 3 is a cross-sectional elevation view of the column encasing in theperforated liner with the commencement of the washing of the surroundingmineral deposit.

DETAILED DESCRIPTION OF THE INVENTION The present invention isparticularly applicable to solution mining of mineral deposits which areoverburdened with an unconsolidated formation. The bed of mineral to besolution mined is shown in FIG. 1 with a shortened view of the prevalentoverburden 107. The mineral deposit may, in effect, be a very thinformation as compared with the thickness of the overburden 107. Thethickness and weight of the overburden are necessary considerations inthe determination of the size of roof bolt and column to be employed butdo not represent a restriction upon any embodiment of this invention.

The solution mining operation is effected by drilling to and slightlyinto the mineral deposit 105. The extent of penetration of the mineraldeposit is dependent upon the size of the roof bolt required. Generally,penetration of 10 percent of the mineral deposit by the drill bit willallow adequate exposure of the mineral deposit from which material maybe removed. The washing process is begun by introduction of a string oftubing 104 into the drilled cavity in the mineral deposit 105. Apredetermined amount of material is then washed about the exposed casingand tubing string. An appropriate volume of material is removed fromabout the roof and the surrounding area of the tubing string 104 to forma cavity 106 in the mineral deposit 105. Casing is then introduced intothe cavity and cemented to the roof, the mineral deposit 105 andwellbore 101. The tubing string 104 is withdrawn after introduction ofthe cement.

When the cement is hardened the well is repenetrated by the drill bitand the well is continued by drilling through the cap of the roof bolt.The respective roof bolt is formed, consisting of casing 202, liner 203and cap 208 as shown in FIG. 2. The washing of the mineral deposit 205is continued by re-entering the tubing string 204 through the drilledroof bolt cap 208. The washing may continue to the point that no furthereconomic recovery of material can be obtained.

It may become necessary in the solution mining of large seams ofmaterial with weak overburden structures to provide more support thancan be derived from the use of the roof bolt type supporter. Under theseconditions the extended cavity 209 in FlG. 2 washed out by the solutionmining process is controlled so as to form a cylindrical cavity from theroof to the floor of the mineral deposit 205. The cylindrical cavity isformed by the progressive lowering of the tubing string during thewashing process so that an evenly washed volume is removed from the roofto the floor of the mineral deposit 205. A casing 310 havingperforations 313 and 314 as shown in FIG. 3 is then set from a pointsomewhat above the roof of the A preferred embodiment of the inventionis to construct the cement column 311 of a permeable cement, such asgravelbased mix, which will allow injection and removal of the washingfluid used in the subsequent solution mining operation. Anotherpreferred embodiment of the invention is to force the washing fluid orsome other fluid through the perforations in the casing as the sealantis setting to leave perforations in the column 311, thus enhancing thefurther solution mining process. Still another preferred embodiment ofthe present invention is to perforate the hardened sealant by chemical,explosive or mechanical means before continuation of the solution miningprocess so as to provide an unrestricted area for the flow of washingfluid and recovered material to and from the wellbore.

After the column has been constructed tubing string is reintroduced andpacked off or segregated by isolation means 312 at a given interval inthe mineral deposit. Use of a packing gland would represent a typicalmeans of isolating the tubing string. Washing fluid is then introducedthrough the perforated casing 310 and column 311 as shown by the flowlines in FIG. 3 and solution mining of the surrounding area 305 isbegun.

The solution mining operation is conducted by introducing washing fluidinto the tubing string 304 at the surface. The washing fluid exits atthe well bottom and is forced through the lower perforations 314 incasing 310. Washing fluid is restricted from directly returning throughthe well annulus by isolation means 312. The washing fluid, therefore,flows outwardly through column 311 either due to the permeability of thesealant material or induced perforations as previously discussed. Thewashing fluid then contacts the mineral deposit thereby dislodging itfrom the seam of material. Both washing fluid and "mineral returnthrough the upper portion of column 311 and perforations 313 to wellbore301 and continue of the annulus to the surface where the mineral isseparated from the washing fluid.

lt will be understood and appreciated by those familiar in the art thatthe solution mining may be accomplished by either roof bolting, columnbuilding or a combination of both as described herein. The novelty ofthe present invention, however, is the method of construction and use ofthe roof bolts and columns to enhance the solution mining operation. Theactual method of solution mining of the mineral deposit to be mined,such as interwell washing, is not a criteria of the invention.

When the present invention is applied to the art of solution mining itprovides for an effective means for the supporting of overburden inorder that a large areal extent of mineral deposit may be recovered. Theinvention enhances the art of solution mining by allowing a cheap andfacilemethod for mining mineral deposits from subterranean mineraldeposits.

The present invention as has been described herein with respect to theparticular embodiment thereof will be appreciated by those skilled inthe art, however, various changes and modifications can be made withoutdeparting from the scope of the appended claims.

Therefore, I claim:

1. In a method of construction for the supporting of overburdened rockduring mining of subterranean mineral deposits in which a well isdrilled into the mineral deposit and a cavity is washed in said mineraldeposit through which casing is introduced into the well, therebyforming an annulus between the wall of the well and the casing andfilling said cavity and annulus with a sealant, thereby sealing saidcasing to the wall of the well and overburdened rock forming a supportin the form of a roof bolt, the improvement which comprises:

a. drilling through the cap of the roof bolt; b. washing a cylindricalcavity from the support to the floor of the mineral deposit; c.introducing easing into said cavity; and d. filling the annulus fonnedbetween said cylindrical cavity and said casing with a sealant, therebyforming a column to support further mineral recovery operations. 2. Themethod of claim 1 in which said sealant for sealing said casing iscement.

3. The method of claim 1 in which:

a. said casing is perforated; and

b. said sealant for sealing said casing is a permeable cement so thatfurther mining may be conducted through the support well.

4. The method of claim 1 in which said casing is perforated and saidsealant is cement which has been previously perforated in a manner thatthe well and mineral deposit are in direct communication through saidperforated casing and said cement column so that further mining can beconducted through the support well.

5. The method of claim 4 in which;

a. the well was drilled into the mineral deposit so that about 10percent of the total thickness of the said deposit exposed to thewellbore; and

b. the cavity washed is hemispherical in shape with the sphericalportion thereof extending downwardly from the roof of said mineraldeposit so that the subsequent filling of said cavity and annulus withsealant forms a cap and roof bolt which will support further mineralrecovery operations for the washing of the cylindrical cavity from thecap of the roof bolt to the floor of the mineral deposit.

6. A method of construction for the supporting of overburdened rockduring mining of subterranean mineral deposits comprising:

a. drilling a well to the floor of the mineral deposit;

b. washing a cavity from the roof to the floor of the mineral deposit;

c. introducing casing into the well, thereby forming an annulus betweenthe well wall and the casing and the wall of the cavity and the casing;and

d. filling the cavity and annulus with sealant, thereby sealing thecasing to the well wall and overburdened rock forming a support so thatcontinued mining is enhanced in that no caving or slouching of theoverburdened rock will occur as further mineral deposit is recovered.

7. The method of claim 6 in which:

a. said casing is perforated; and

b. said cement for sealing said casing is a permeable cement so thatfurther mining can be conducted through the support well.

8. The method of claim 6 in which said casing is perforated and saidcement has been previously perforated in a manner that the well andmineral deposit are in direct communication through said perforatedcasing and column so that further mining can be conducted through thesupport well.

9. The method ofclaim 6 in which the sealant for sealing the casing iscement.

10. The method of claim 6 in which the cavity washed is cylindrical.

1. In a method of construction for the supporting of overburdened rockduring mining of subterranean mineral deposits in which a well isdrilled into the mineral deposit and a cavity is washed in said mineraldeposit through which casing is introduced into the well, therebyforming an annulus between the wall of the well and the casing andfilling said cavity and annulus with a sealant, thereby sealing saidcasing to the wall of the well and overburdened rock forming a supportin the form of a roof bolt, the improvement which comprises: a. drillingthrough the cap of the roof bolt; b. washing a cylindrical cavity fromthe support to the floor of the mineral deposit; c. introducing casinginto said cavity; and d. filling the annulus formed between saidcylindrical cavity and said casing with a sealant, thereby forming acolumn to support further mineral recovery operations.
 2. The method ofclaim 1 in which said sealant for sealing said casing is cement.
 3. Themethod of claim 1 in which: a. said casing is perforated; and b. saidsealant for sealing said casing is a permeable cement so that furthermining may be conducted through the support well.
 4. The method of claim1 in which said casing is perforated and said sealant is cement whichhas been previously perforated in a manner that the well and mineraldeposit are in direct communication through said perforated casing andsaid cement column so that further mining can be conducted through thesupport well.
 5. The method of claim 4 in which; a. the well was drilledinto the mineral deposit so that about 10 percent of the total thicknessof the said deposit exposed to the wellbore; and b. the cavity washed ishemispherical in shape with the spherical portion thereof extendingdownwardly from the roof of said mineral deposit so that the subsequentfilling of said cavity and annulus with sealant forms a cap and roofbolt which will support further mineral recovery operations for thewashing of the cylindrical cavity from the cap of the roof bolt to thefloor of the mineral deposit.
 6. A method of construction for thesupporting of overburdened rock during mining of subterranean mineraldeposits comprising: a. drilling a well to the floor of the mineraldeposit; b. washing a cavity from the roof to the floor of the mineraldeposit; c. introducing casing into the well, thereby forming an annulusbetween the well wall and the casing and the wall of the cavity and thecasing; and d. filling the cavity and annulus with sealant, therebysealing the casing to the well wall and overburdened rock forming asupport so that continued mining is enhanced in that no caving orslouching of the overburdened rock will occur as further mineral depositis recovered.
 7. The method of claim 6 in which: a. said casing isperforated; and b. said cement for sealing said casing is a permeablecement so that further mining can be conducted through the support well.8. The method of claim 6 in which said casing is perforated and saidcement has been previously perforated in a manner that the well andmineral deposit are in direct communication through said perforatedcasing and column so that further mining can be conducted through thesupport well.
 9. The method of claiM 6 in which the sealant for sealingthe casing is cement.
 10. The method of claim 6 in which the cavitywashed is cylindrical.